Scanning electron microscope having time constant measurement capability

Abstract

In a scanning electron microscope, an optimum scanning method for reducing the amount of deflection of a primary electron beam and secondary electrons is determined to acquire stable images. An energy filter is used to discriminate between energy levels. The change in yield of obtained electrons is used to measure the variation in specimen potential. The time constant of charging created during electron beam irradiation is extracted. The scanning method is optimized based on the extracted time constant to reduce the distortion and magnification variation that appear in a SEM image.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to an electron microscope that uses an electron beam to observe a specimen, and for example to a scanning electron microscope that detects electrons emitted from a specimen under electron beam irradiation to measure or examine the shape and composition of the specimen.[0003]2. Background Art[0004]Miniaturization and large-scale integration of ULSI (Ultra-Large Scale Integration) elements have been accelerated, so that devices are now processed at dimensions of several tens of nanometers. Furthermore, there have been increasingly developed multilayered devices using various types of new materials, such as low dielectric constant films and metal gate films to achieve higher speeds, as well as three-layer resist films to enhance etching resistance. To this end, tighter critical dimension (CD) management during ULSI processing has been required.[0005]In semiconductor processing steps, insulator...

AI Technical Summary

Benefits of technology

[0016]The present invention has been made in view of such circumstances and aims to provide a scanning electron microscope capable of acquiring stable images by determining an optimized scanning method in which the amounts of deflection of the primary electron beam and secondary electrons are reduced.

[0026]According to the present invention, an optimum scanning order (most resistant to the influence of charging produced by electron beam irradiation) can be determined, and accurate, stable images can be acquired by scanning a specimen in the scanning order.

Problems solved by technology

The charged specimen not only changes the amount of secondary electrons that attempt to escape from the surface of the specimen but also bends the trajectory of the primary electron beam, resulting in distortion of images obtained by a scanning electron microscope.

As a result, it is difficult to measure true dimensions and shapes after processing.

For example, in the case of an ArF resist, it cannot be judged whether line edge roughness (LER) has occurred in an etching step or charging in the electron microscope has caused an error in dimension measurement.

There are also problems in observation of contact hole having a large aspect ratio, such as distortion of the observed shape of the contact hole, and difficulty in identifying whether the observed hole diameter is either the upper or lower diameter.

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